1. Field of the Invention
2. Discussion of the Background
A manually operated pump for dispensing liquids under pressure, particularly suitable for use on transparent containers in which the pump body must be as little visible as possible.
Many types of manually operated pumps are known for dispensing pressurized liquids drawn from a container via a unidirectional suction valve and expelled via a discharge valve which is closed when in its rest position and is opened by the liquid which is put under pressure within the interior of the pump when its stem is manually operated or lowered.
In most pumps the suction valve is positioned within an elongate tubular appendix extending outside the main pump body, on this appendix there being mounted one end of a tube through which the pump draws the liquid contained in the container on which the pump is mounted. These pumps have the characteristic of a considerable length compared with the pump transverse dimensions.
U.S. Pat. Nos. 5,503,306 and 5,505,343 describe pumps in which the suction valve is formed from a movable ball housed at the free end of a tubular appendix which extends inside the main pump body, about a hole provided in the base wall of the pump, the ball being able to seal against a seat provided at the free end of this appendix, within the interior of the pump body.
The pumps described in both U.S. Pat. Nos. 5,503,306 and 5,505,343 are formed in such a manner as to expel (when operated) practically all the liquid contained in the pump. For this purpose, as can be clearly seen from the drawings of the two said patents, the pump body must have a very elongate shape, with the piston which forms part of the operating stem of each pump being very long (compared with the general pump dimensions) and tightly sliding along a cylindrical surface (of the fixed pump body) which is also very long, as is also the tubular appendix against the end of which the said ball seals to form the unidirectional valve for drawing the liquid into the pump. The result is that the pumps described in the two cited US patents have a longitudinal dimension much greater than their transverse dimension.
All the aforesaid pumps can be easily used on most containers for liquids to be dispensed, but cannot be mounted on very short containers. Moreover, these pumps are clearly visible by the user when mounted on containers made of transparent material, this being unacceptable for certain uses in which the outer appearance of the container is very important (for example in the quality perfume field), to the extent that the constituent material of the container is often made opaque or coloured or covered with labels or the like to hide the pump body mounted on it.
Many types of discharge valve are also known for enabling the liquid contained in the pump to pass through the pump stem when the pressure of this liquid reaches and exceeds a predetermined value (this to prevent the liquid dripping from the discharge hole in the pump operating head) at the beginning and end of liquid delivery respectively.
In the pumps described in both U.S. Pat. Nos. 5,503,306 and 5,505,343 the discharge valves are formed from a very long cylindrical rod housed and movable within the bore of the stem of the respective pump, in this bore there being provided longitudinal grooves or recesses defining thin longitudinal channels with the opposing surfaces of the said cylindrical rods. Because of their very small cross-section and their relatively large length, said longitudinal channels cause large pressure drops which brake the flow of the liquid in them, to reduce the pressure with which it leaves the bore of the pump stem, with consequent dripping of the liquid from the discharge hole in the pump operating head, both at the beginning and at the end of delivery.
In addition, in the pumps described in the two said US patents, the discharge valve is sealed merely by a portion of its constituent cylindrical rod being simply urged by a spring against a bearing surface provided in a corresponding seat of each stem. The result is both that the seal is very precarious and that the liquid starts to pass through the valve gradually as soon as it begins to open, this passage being very small at the beginning and end of delivery, with consequent further pressure drop and dripping of the liquid from the hole in the operating head.
EP-A-0289856 and U.S. Pat. No. 5,192,006 describe pumps the discharge valves of which consist of a rod housed and movable within the bore of the respective pump stem, this bore having a short cylindrical portion from which longitudinal ribs or grooves extend. A seal lip projects from the rod to sealedly slide along a cylindrical portion of the stem bore, and to open liquid passage only when the lip has moved above said ribs or grooves, in order to enable the liquid to begin to flow out at a pressure greater than that required to cause initial movement of the rod. However even in this case the opening and closure of the discharge valve is initially gradual, with the aforestated drawbacks.